Interior residential and light commercial wall and flooring systems commonly include plywood or oriented strand board (OSB) nailed to a wooden frame or mechanically fastened to a metal frame. OSB consists of pieces of wood glued together. Regardless of whether the frame of a building is constructed from wood and/or steel, such frame structures are commonly subjected to a variety of forces. Among the most significant of such forces are gravity, wind, and seismic forces. Gravity is a vertically acting force while wind and seismic forces are primarily laterally acting. Not all sheathing panels are capable of resisting such forces, nor are they very resilient, and some will fail, particularly at points where the panel is fastened to the framing. Where it is necessary to demonstrate shear resistance, the sheathing panels are measured to determine the load which the panel can resist within the allowed deflection without failure.
The shear rating is generally based on testing of three identical 8×8 feet (2.44×2.44 m) assemblies, i.e., panels fastened to framing. One edge is fixed in place while a lateral force is applied to a free end of the assembly until the load is no longer carried and the assembly fails. The measured shear strength will vary, depending upon the thickness of the panel and the size and spacing of the nails or mechanical fasteners used in the assembly. The measured strength will vary as the nail or mechanical fastener size and spacing is changed, as the ASTM E72 test provides. This ultimate strength will be reduced by a safety factor, e.g., typically a factor of two to three, to set the design shear strength for the panel.
As the thickness of the board affects its physical and mechanical properties, e.g., weight, load carrying capacity, racking strength and the like, the desired properties vary according to the thickness of the board.
U.S. Pat. No. 6,620,487 to Tonyan et al., incorporated herein by reference in its entirety, discloses a reinforced, lightweight, dimensionally stable structural cement panel (SCP) capable of resisting shear loads when fastened to framing equal to or exceeding shear loads provided by plywood or oriented strand board panels. The panels employ a core of a continuous phase resulting from the curing of an aqueous mixture of calcium sulfate alpha hemihydrate, hydraulic cement, an active pozzolan and lime, the continuous phase being reinforced with alkali-resistant glass fibers and containing ceramic microspheres, or a blend of ceramic and polymer microspheres, or being formed from an aqueous mixture having a weight ratio of water-to-reactive powder of 0.6/1 to 0.7/1 or a combination thereof. At least one outer surface of the panels may include a cured continuous phase reinforced with glass fibers and containing sufficient polymer spheres to improve nailability or made with a water-to-reactive powders ratio to provide an effect similar to polymer spheres, or a combination thereof.
U.S. Pat. No. 6,241,815 to Bonen, incorporated herein by reference in its entirety, also discloses formulations useful for SCP panels.
One form of wallboard structure purportedly for metal construction applications is disclosed in U.S. Pat. No. 5,768,841 to Swartz et al. That wallboard structure has a metal sheet attached to an entire side of a gypsum panel with an adhesive. Another wallboard panel is disclosed in U.S. Pat. No. 6,412,247 to Menchetti et al. The International Building Code in its “Steel” section also references the use of shear walls utilizing panel type members, i.e., drywall, steel plates and plywood, etc.
US patent application publication no. 2005/0086905 A1 to Ralph et al. discloses shear wall panels and methods of manufacturing shear wall panels. Various embodiments comprise wallboard material employed with a sheet stiffener in the form of a plate to form a wall panel that may be used in applications wherein shear panels are desired.